FIGS. 1 and 2 show a wafer cleaning apparatus for cleaning the surface of a processed object 10. The processed object 10 is a wafer or another object. The wafer cleaning apparatus utilizes a first pivotal rod set 20 and a second pivotal rod set 30 to clamp the periphery of the processed object 10, and utilizes pivotal rods 21 of the pivotal rod sets 20 and 30 to support and rotate the processed object 10. There are also two cleaning wheels 40, which are respectively moved to upper and lower end faces of the processed object 10 and rotate to clean the processed object 10.
As shown in FIG. 3, during the maintenance of the wafer cleaning apparatus, the spacing between the first pivotal rod set 20 and the second pivotal rod set 30 is adjusted to adjust a force for clamping the processed object 10, and a level 50 is placed at the upper end face of the processed object 10 to determine whether the processed object 10 clamped between the pivotal rod sets 20 and 30 is level.
However, the above conventional apparatus and a method thereof for adjusting the clamping force of a processed object have the following drawbacks.                1. The above conventional device and the method thereof for adjusting the clamping force of a processed object utilize the level 50 as a adjustment tool, and experiences are exploited to determine whether the processed object 10 clamped between the pivotal rod sets 20 and 30 is level, thereby adjusting the force for clamping the processed object 10 between the pivotal rod sets 20 and 30. The force for clamping the processed object 10 between the pivotal rod sets 20 and 30 cannot be obtained in quantitative way. Therefore, the adjustment of the clamping force of the pivotal rods is inconvenient.        2. The above conventional device and the method thereof for adjusting the clamping force of a processed object utilize the level 50 for adjustment of the force for clamping the processed object 10 between the pivotal rod sets 20 and 30. Accumulation and teach-and-learn of experiences are required. The operation cannot be performed with standardized steps or procedures.        3. The above conventional device and the method thereof for adjusting the clamping force of a processed object may easily result in a too small force for clamping the processed object 10 between the pivotal rod sets 20 and 30 due to misjudgment so that the processed object 10 cannot synchronously rotate with the pivotal rod sets 20 and 30, or may easily result in a too large force for clamping the processed object 10 between the pivotal rod sets 20 and 30 so that the processed object 10 will hog. The two cleaning wheels 40 will respectively abut against two sides of the processed object 10, hence easily causing breakage of the processed object 10 and damage of the cleaning equipment.        